This invention relates to a magnetic head using a magnetic disk device, and in particular to a spin valve magnetic head which has high sensitivity, reproduction stability and manufacturing yield. Here, the term spin valve magnetic head refers to a type of magnetic head with a magnetic resistance effect, wherein the electrical resistance of the head changes due to the variation of the angle between the magnetization direction of a fixation layer pinned by an antiferromagnetic layer and the magnetization direction of an unconstraint layer due to an external magnetic field.
To increase the reproduction sensitivity of a reproducing magnetic head, a magnetic head has been disclosed comprising a spin valve film having a sandwich structure wherein a pair of magnetic layers are laminated on either side of a non-magnetic layer on a substrate. In the spin valve film, the magnetization of one magnetic layer (fixation layer) is fixed in the element height direction by an exchange field with an adjacent antiferromagnetic layer, but the magnetization of the other magnetic layer (unconstraint layer) is a single magnetic domain in the track width direction of the element generally obtained by hard bias using the field of a permanent magnet, and rotates freely due to an external magnetic field.
The fixation layer can be magnetized in a single magnetic domain more satisfactorily the larger the unidirectional anisotropic magnetic field due to the antiferromagnetic layer. Linearity of magnetic response relative to an external magnetic field is better maintained the more its magnetization is fixed, and the characteristics of the magnetic head are thereby improved. For this purpose, various antiferromagnetic materials have been proposed in the art. The characteristics of the antiferromagnetic material are also known to vary according to the material of which its base is composed.
For example, in Japanese Patent Laid-Open Hei 8-315326, a magnetic resistance head is disclosed whereof characteristics such as magnetic resistance change ratio are improved by disposing a crystalline soft magnetic film which has high resistance and which can improve magnetic alignment as the base of a magnetic resistance effect film. In the same disclosure, a non-magnetic metal film such as Ta is provided in the base to increase the crystallinity of the crystalline soft magnetic film. Also, Japanese Patent Laid-Open Hei 8-213238 describes a magnetic resistance sensor using a Ta underlayer to obtain a crystal orientation of the magnetic unconstraint layer.
In Japanese Patent Laid-Open Hei 9-16915, in a spin valve magnetic resistance transducer, two layers comprising a Ta film and NiFe alloy film as underlayer are used to improve the crystallinity of the antiferromagnetic layer, and obtain a linear magnetic resistance change ratio by sufficiently fixing the magnetization of the fixation layer. In Japanese Patent Laid-Open 6-325934, in a magnetic resistance effect device, a two-layer underlayer, comprising a second underlayer such as Ta is placed between a first underlayer of a material having a fcc lattice and a substrate, to improve the (111) orientation of a ferromagnetic film formed thereon and improve surface flatness and smoothness.
In Japanese Patent Laid-Open 2000-150235, a first underlayer of Ta and a second underlayer of NiFeCr are laminated on a substrate. The NiFeCr film has an fcc structure and by giving it a (111) orientation, the (111) orientation of the unconstraint layer, non-magnetic electroconducting layer, fixation layer and antiferromagnetic layer formed thereon is intensified.
As a result, the unidirectional anisotropic magnetic field is increased and the mutual interactive magnetic field between the two magnetic layers is reduced, so a high magnetic stability is obtained, and magnetic conversion properties such as a high magnetic resistance change ratio and magnetic resistance variation linearity, are enhanced.
In U.S. Pat. No. 6,141,191, when NiFeCr or NiCr is used as a base film, the crystal particle size of the unconstraint layer, non-magnetic layer, fixation layer and antiferromagnetic layer which are sequentially grown thereupon increases, so interlayer diffusion is suppressed and thermal stability improves. Also, the overall sheet resistance of the film decreases while the resistance variation amount and resistance change rate increase, which is an advantage for high sensitivity.
To achieve high recording densities, as tracks become narrower, a demand has emerged for high sensitivity and noise reduction. To reduce noise, it is effective to reinforce the magnetic domain control of the unconstraint layer, but the magnetization of the unconstraint layer is then not easily manifested. Also, as a secondary effect, the vertical bias field tends to affect the magnetization direction and leads to a decline of reproduction output. Therefore, it is difficult to attain the dual objectives of reproduction stability and reproduction sensitivity.
The use of a NiFeCr layer or NiCr layer as underlayer resolves this problem as it increases the unidirectional anisotropic magnetic field, increases the resistance change rate and improves thermal stability, hence it is now being proposed as a way of achieving both reproduction stability and reproduction sensitivity.
However, when this is applied to an actual magnetic head, in the NiFeCr or NiCr single layer base, properties easily change depending on the substrate material or surface roughness, and as the optimum composition range is narrower, it is difficult to continually obtain the same characteristics.
On the other hand, in a Ta/NiFeCr or Ta/NiCr two-layer base in which Ta is inserted between a substrate and NiFeCr or NiCr, it was found that although the effect of the substrate can be eliminated, the required film thickness increases. Further, the optimum composition range is also narrow and the coercive force of the unconstraint layer is large.
It is therefore an object of this invention to provide a spin valve magnetic head having the basic structure of an antiferromagnetic layer, fixation layer, non-magnetic layer and unconstraint layer on a substrate, wherein an underlayer is provided having a laminated structure comprising a first underlayer of Ta, a second underlayer of NiFeCr and a third underlayer of NiFe interposed between the substrate and the basic structure.
It is a further object to provide a dual spin valve magnetic head having the basic structure of a first antiferromagnetic layer, first fixation layer, first non-magnetic layer, unconstraint layer, second non-magnetic layer, second fixation layer and second antiferromagnetic layer, wherein an underlayer is provided having a laminated structure comprising a first underlayer of Ta, a second underlayer of NiFeCr and a third underlayer of NiFe interposed between the substrate and the basic structure.
As the second underlayer used in the above spin valve film, NiCr can be used instead of NiFeCr.
It is effective from the viewpoint of improving characteristics if the crystal structure of the NiFeCr or NiCr in the second underlayer is a bcc structure.
It is desirable that the crystal structure of the NiFeCr or NiCr in the second underlayer is bcc, and is oriented in the (110) direction.
In addition, it is desirable that the average crystal particle size of the NiFeCr or NiCr in the second underlayer measured in the in-plane direction is at least 10 nm.
In the NiFeCr which is the second underlayer in the underlayers of the aforesaid spin valve film, it is preferred that the elements in the empirical formula (Nia-Feb)x-Cry are in the ranges 45 less than a less than 100, 55 less than b less than 100, 50 less than x less than 80, 20 less than y50, a+b=100, x+y=100 in terms of at %, and the film thickness is 4 nm-6 nm.
Also, when NiCr is used as the second underlayer, it is preferred that the elements in the empirical formula NixCry are in the ranges 50 less than x less than 80, 20 less than y less than 50, x+y=100 in terms of at %, and the film thickness is 4 nm-6 nm.
In an NiFe underlayer, which is a third underlayer that can be combined with NiFeCr or NiCr, the elements represented by the empirical composition Nix-Fey are in the ranges 70 less than x less than 90, 10 less than y less than 30, x+y=100 in terms of at %, and it is convenient that the film thickness is 0.3 nm-1.5 nm. It is preferred that the film thickness of Ta which is the first underlayer is at least 0.3 nm.
The unconstraint layer in the spin valve film contains a magnetic layer of Co or CoFe alloy. More specifically, the unconstraint layer may possibly be a Co layer or CoFe alloy layer, but a layered structure with a Co layer, CoFe alloy layer or another type of magnetic layer such as a NiFe alloy, or layered structures with non-magnetic layers such as Cu and Ru, are also possible.
The fixation layer comprises a magnetic layer of at least two layers separated by a non-magnetic layer such as Ru. The magnetic layers forming the fixation layer are joined so that the magnetic moments are antiparallel. The antiferromagnetic layer may be PtMn, NiMn, IrMn or PdPtMn.